Intermittent combustion gas turbine engine



June 5, 1956 R. H. MARcHAL ET AL 2,748,564

INTERMITTENT COMBUSTION GAS TURBINE ENGINE Filed March 7, 1952 2 Sheets-Sheet l June 5, 1956 R. H. MARCHAL ET A1. 2,748,564

INTERMITTENT coMusTroN GAS TURBINE ENGINE 2 Sheets-Sheet 2 Filed March '7, 1952 vthese -gases 'by vair ,from the ,'compressor.

'prise any air compressor or turbine.

United States Patent O -z,74s,s64

INTERMTTENT coMBUsrroN :GAS TURBINE ENGINE Raymond H. Marchal, Paris, FranoisG. IParis, Chaville, Jean Bertin, Neuilly-sur-Seine, and Louis A. I. Bauger, Vanves, France, assgnors Vto Societe Nationale dEtude et de Construction de Moteurs dAviation, Paris, France, a company of France Application March 7, 1952, Serial No. 275,312

Claims priority, application France-March 1'6, 1951 '1 claims. (ci. s0-35.6)

Gas-turbine engines are Vusually of the constant-pressure cycle type, i. e. the whole amount 'of air required by the engine is compressed, in the compressor of -the engine, vup to a certain pressure Ylevel which is maintained during combustion of fuelwithin this air. vThis combustion which takes place at a Asubstantially constant lpressure, Ais effected -inside combustion -chambers to 'which air and fuel are supplied in a 4 constant mass ratio, thus ensuring continuous combustion.

The burnt gases resulting from combustion are at a very high temperature in the combustion chambers'(2'200 to 2509" -C.). Their temperature at the outlet of these chambers Ais lowered to /a convenientivaluewi'thregard to the 4mechanical strength of the materials, Iby 1a ldilution of The ow of these gases `vthrough the dcombustion fchambers gives rise to va ypressure loss; -in other Words, 'the pressure 4at the outlet of the chamber is 'lower than the inlet pressure of the air.

When expanding through the turbine, the gases'supply the energy required for driving the compressor and it is possible to use the 4excess energy of the gases by expanding them further. This can lbe effected in the turbine (or in a further turbine -or turbine wheel), a's inthe case lof stationary plants, or power plants of ships and locomotives or aircraft engines -known as Yturbo-propellers; alternatively -the expansion can take place "in a propulsion nozzle thus converting the `potential -for -pressureenergy still available into kinetic energy whichris usedfor propeiling a movable body by reaction, as in Vthe case of turbojetengines.

Jet propulsion -engines are known which do not com- The'se engines are called pulse jet units -and include `a resonant-iiring-combustion l'chamber fed with fuel and air at `atmospheric pressure (this air `supply being effected 'through y-valve means or an inlet'a-llowing free "flow of Lair towards `the chamber while `hindering back "flow Iofcomlmstion v-gas inthe opposite direction) and-a rearwardly ldirec-ted exhaust pipe allowingthe combustiongases to .expand and imparting ythereto 'a'highvelocitv Combustion takes place in a pulsatory way which is automatically sustained-atthe frequency of a sound lpipe of similar design as said unit, that is to say `at a proper .frequency depending on the length of the unit. The exhaust pipe is not `.only,designed .for imparting velocity tothe .pulses of.,com,bustion gas butalso for `ensuringscavenging .ofthe Acombustion.Charnber Y.bycreating therein a .vacuum ,due .to the Vpulses of `combustion gas travelling rapidly through ithe .exhaust pipe and thereby acting as gaseouskpistons.

Asttbetcornbustion cycle. is performed, inv-these resonanttiring .combustion chambers, .at :a substantially constant volume,.pressure.rises inithe chamber duringcombustion. This `increase Ain pressure vin the chamber .gives :n.se, Vat the outlet of zthefexhaust pipe, stoapulse oftburntgases atfhigh velocity, i. e. rhaving a large amount of kinetic put shaft of this turbine.

2,748,564 Patented June 5, 1956 ICC atmospheric air at normal temperature and pressure,

amounts to about -8 to 110% of the ytotal heat energy introduced into the combustion chamber.

The object kof the present invention is to apply such pulsatory combustion chambers to gas-turbine engines provided with an air-compressor. 4

These charnbers being fed with air under pressure discharged 'Yby the compressor, the increase in pressure and temperature ofthe air delivered, dueto the previous compression effected by the compressor, further increases the percentage of heatl energy converted into kinetic vfenergy in the exhaust pipe. This-is ldue to the '-fact that the combustion is improved, Vin an atmosphere under 'pressure, 4which results, vin the chamber, Ain a further increase in pressure during combustion at substantially constant volume.

VBy ydirecting the high `velocity pulses of gases issuing from the exhaust pipe, towards the blades of a turbine adequately designed for using `the kinetic energy` of the motive fluid, -'it vis possible Ato convert the kinetic energy ofgthe pulsesinto Jmechanical 'energy available at the out- The gases issuing from this Vturbine lhave a high static pressure, and lcan therefore -performwork at constant press-ure, in one or more turbine wheels, or in a jet-propulsion nozzle, 'or in both.

kif it is 4assumed that the e'iciency amounts to 50% A(a rather `moderate value which can be undoubtedly exceeded), Vfor Athe conversion of the kinetic energy of the pulses into mechanical energy, a'fraction equal to 5% of the "total heat energy introduced into the combustion chambers will be recovered and added to the shaft of the engine; this lpercentage corresponds to an increase of 2() to 25% of available power and of heat eicieney (i. e. ofthe fuel consumption) as ycompared with a conventional engine operating vwith thcsam'e cycle. v

The object of the present invention is to provide a gas-turbine engine ycomprising a primary uturbine wheel 'of the Vimpulse-type or operating with-a certain degree of reaction, van "air compressor and one or more pulse jet units which vare Vfed with'air by the compressor and-provided ',w'it-h Aau exhaust pipe opening towards a part of 'the stationary Vblades arranged ahead of said turbine wheel, ,the pipeof each unit being adapted to transform Ainto kinetic energy Yat least dthe energy vwhich'corresponilsiwith the pressure waves in the corresponding combustion chamber.

A further object of the invention is to Iprovide mea ns lfor using the ,residual energy `under constantpressure re- -know/min such-turbines `thercis either no change in pres-` sure `as the gases pass'the blade-,ring (e. g. Vimpulse turbines) or a minor decrease in pressure (e. g. reaction turbines). 'Velocity-absorbing turbines are therefore distinct -from expans'ion turbines lwhich l are operated -essen-tially-by-the pressure of @the gases, these turbines-being designed 4,for converting :the :pressure energy of the fgases in tofwork.

When an impulse turbine is used, the static pressure of the fluid is the same at the discharge end of the compressor, at the inlet of the stator blades and at the outlet of the impulse turbine wheel.

An advantage of this embodiment is that the manifold collecting the exhaust gases of the turbine can be directly connected to the discharge end of the air compressor, thus facilitating dilution of the gases and cooling them before they are made to work in expansion turbine or turbines.

Thus, a continuous ow of hot gases at constant pressure issues from the velocity-absorbing turbine and is made to expand in the remainder of the engine.

Other objects and advantages of the invention will be apparent during the course of the following description.

In the accompanying drawings in which like reference characters are employed to designate like parts through out the same,

Fig. 1 is a diagrammatic axial section of a form of aircraft turbopropeller, according to the invention,

Fig. 2 is a cross-section taken along line II-II of Fig. 1,

Fig. 3 is graph showing the variations in pressure in the combustion chambers in terms of time,

Figs. 4 and 5 are diagrammatic developed views of nozzles at the outlet of the exhaust pipes and of the stator blades of the impulse turbine.

In the case of an aircraft engine, air is sucked up through the diffuser 1 which converts into pressure the kinetic energy of the air due to the speed of the aircraft. This air is then compressed in a compressor 2 which is of the radial-flow type in the example illustrated but .which may be of the axial-flow or helical type. At the outlet of the compressor, the air under pressure is collected in an annular manifold 3 and supplied to the pulsatory combustion chambers 4 located around the shaft of the engine. By means of a ring of vanes 21 pivoting about axes 21a and disposed in the intake to the compressor, it is possible to adjust the pressure ratio and the output of the compressor. This arrangement ensures an easy crossing of the rather delicate surging zone when the engine is started. The vanes also allow of reduced rates of operation of the turbine whilst maintaining a high eciency of the compressor. They therefore provide a great flexibility to the engine. manifold 3, air under pressure is introduced into each combustion chamber 4 through a freely open inlet or duct 6 adapted to have a low resistance to flow in the feed-direction towards the chamber 4 and a high resistance in the opposite direction, this duct thus forming a kind of aerodynamic valve. Various types of such ducts are known at present.

At the end of each chamber opposite the inlet duct 6, there is provided an exhaust pipe ending with an expansion nozzle 5.

The pulsatory chambers 4 are continuously supplied, during operation, with a convenient fuel: e. g. gasoline, petrol, oil, fuel-oil, pulverised coal, etc. 'This fuel is fed through a duct 4a into which it is discharged by a pump (not shown). The chambers are connected to each other by tubes 22. The first ignition may be effected by means of a spark-plug and the subsequent ignitions automatically occur due to the previous combustion pulse. The successive combustions or explosions automatically adjust themselves to the frequency of the sound pipe which every chamber forms. During each combustion which takes place at substantially constant volume, the pressure rises in the chamber and the burnt gases rush through the nozzle (they cannot escape through the inlet duct 6, or at any rate an appreciable fraction of them, owing to the constitution of this duct). Toward the end of each combustion, the expansion wave gives rise to a depression in the chamber. This depression promotes intake into the chamber, through 6, of the air under pressure from the manifold 3, a new combustion occurs, and so forth.

This cycle is illustrated by the diagram of Fig. 3 which shows the graph of the values of pressure obtaining in From the annular q each combustion chamber, in terms of time. P stands for the discharge pressure of the compressor 2, i. e. the feed pressure of the chambers, and Po for atmospheric pressure. T stands for the period of the cycle. The portions of the curve above the horizontal line P correspond to the increase in pressure from P to P1 during each combustion, then its decrease from P1 to P as gas exhaust proceeds. Each of these portions extend over about a third of the period. The portions of the curve below P correspond to the relative vacuum following, in the chamber, the exhaust of the burnt gases, this vacuum giving rise to a further intake of a charge of air.

The volume of the manifold 3 must be large enough, so that, evenif all the chambers 4 suck simultaneously, substantially no pressure drop arises in this manifold. The nozzle 5 at the end of the exhaust pipe of each chamber 4 is so proportioned as to accelerate the burnt gases generated during constant volume combustion, thus making these gases to expand from their maximum pressure Pi to a value approximately equal to the pressure P of the discharge of the compressor. In other words, the nozzles 5 only convert into kinetic energy, the pressure energy corresponding to the pulse, i. e. to the hatched portion of each cycle (Fig. 3).

Beyond the nozzles 5, there are arranged stator blades 7 which impart to the gases the optimum inlet angle with respect to the moving blades of an impulse turbine wheel 8. At the outlet of these blades, the gases have theoretically given up the whole of their kinetic energy and are collected in an annular manifold 9; the pressure obtaining in the latter is the same as that obtaining in the manifold 3 at the discharge end of the cornpressor and this manifold 9 is connected, as will be indicated hereafter, to this end. The potential energy of these gases corresponding to their temperature is then used in a constant inlet pressure turbine or expansion turbine which may include one or more wheels 10. 'Ihe wheels 8 and 10 can be coupled so as to drive together the compressor 2 and possibly an etective power receiving apparatus. The drawing refers to the case wherein the shaft 16 of the compressor driven by the turbines, is extended and drives, through a step-down gearing 17, a propeller shaft 17a.

The impulse turbine wheel 8 has necessarily a large diameter. The reason is that the temperature of the gases at the inlet to this turbine is high, their specific mass is relatively low and since the injection velocity is determined by the velocity at the outlet of the expansion nozzle 5 of each pulsatory chamber 4, the passage crosssection of the blading requires blades of great height. In order to design a high-eieency turbine, the blades of great height require a large diameter disc whose mean tangential velocity must however remain at a convenient value. The consequence is a rotational speed substantially smaller than that of other turbines. The mechanical coupling of turbines with a common power receiving apparatus, such as the compressor 2, must be made through a step-up gearing 15 which allows the angular velocities of the turbines to be taken into account. The shaft 16 of the compressor can be directly connected to the shaft 16a of the turbine 10, whereas the shaft 16b of the impulse turbine 8, which is hollow and surrounds the shaft 16a, is connected to the shaft 16 through the stepup gearing 15.

As in pulsatory combustion operation which is sustained in each chamber 4, the exhaust pulse lasts for about one third of the period, the high-temperature burnt gases are in contact with the blades 8 of the impulse turbine only during a third of the period. In other words, the time allowed for the transfer of heat and its evacuation through the blades of the turbine is twice as long as the time during which heat is evolved. It can be understood hence that the impulse turbine is capable of standing inlet temperatures of gases much higher than those which are usually admissible in the case of con- .5 ventional .gas lturbines of @the continuous iiow ftype. For this zreason, `it will be often lpossible Ato 4operate .fthe .impulse :turbine l.without .diluting .the .burnt Agases 'with fresh air before they are supplied to the blading 8 of .this 'turbine.

In the illustrated embodiment, .dilution .is effected at the exhaust .end of the pulsatory Acombustion chambers, by means of .apertures .18 .in communication with a duct 12 conveying compressed air from the manifold 3. On the drawing, this duct is formed between the combustion chamber walls land a sheathingdisposed thmearound. ln this arrangement, .the dilution `air cools the walls of the chambers.

Anyway dilution is limited, and .this .is an advantage since losses of energy'are unavoidable, and the smaller the mass of dilution air the lower these losses.

In Fig l, it 'has been assumed 'that the axes of the chambers '4, the exhaust pipes and the nozzles 5' were parallel to 'the general axis of Vthe engine; actually these axes are inclined asshown .in the development illustrated .in Fig 4; vit has been further .assumed that .the stator blades 7 are fed from an annular manifold 7a into which all the nozzles S discharge.

Fig. 5 shows another form in which each nozzle extends up to the wheel and encloses several stator blades. The former arrangement is convenient when all the combustion chambers operate in synchronism, the latter arrangement when the chambers are out of phase.

Figs. 4 and 5 further indicate the two ways in which dilution air flows in through the annular apertures 1S. Air is first drawn in, by aspiration effect, by the gas pulse, as indicated oy arrow F. Then, during the vacuum following the pulse in the chamber, air is sucked up thereinto, as indicated by arrow F1.

The blades of the impulse turbine which are preferably made of refractory alloy can be cooled internally by circulation of air. The cooling air may be taken for instance from the dilution air and led to the blades through apertures 20, 29a of the wheel disc.

For this purpose, apertures 23 connect the duct 12 to the chamber 25 which feeds the apertures 20 located on the front face of the turbine disc. The chamber 26 which feeds the apertures Zita located on the rear face of the disc, is connected to the air inlet duct 12 through one or more tubes 24 crossing the manifold 9.

The gases issuing from the impulse turbine and which are no longer pulsatory, are collected in the manifold 9. Their mean temperature reaches a value slightly lower than their temperature at the end of combustion in the chambers 4, but still too high for use in the continuous flow turbines 10. Dilution of these gases with air from the compressor is effected through the apertures 11 connecting the duct 12 to the manifold 9.

Burnt gases issuing from the turbines exhaust through 14. In an aircraft engine such as illustrated, the remainder of their energy is used, in a nozzle 13 which provides an additional thrust.

The accessory parts of the turbine with pulsatory combustion chambers are the same as those of conventional gas turbines.

The machine can be very simply started in the same way as a pulsejet engine. A jet of compressed air is introduced into one of the pulsatory chambers while fuel is injected by Imeans of an auxiliary pump. Ignition in this chamber, or simultaneously in two opposite chambers, will be carried out by means of a spark-plug and pulsatory combustion starts; the impulse turbine will be urged by pulses of hot gases issuing from the chamber, and rotation of this turbine will produce rotation of the compressor and other turbines. All the chambers are then supplied with air from the compressor and with fuel through the agency of the pump (not shown); ignition in the chambers is effected from the rst chamber through the interconnecting tubes 22. The power of the impulse turbine rapidly rises and so does the rotation speed; the

.another chamber.

.and may drive separate power receiving apparatus.

`drive the propeller.

6 constant inlet pressure turbines in their .turnsupply `.power and the turbine is started. The injection of air and .fuel into the starting chamber (or two chambers) .is stopped. Hence, starting does not require, as in the case of conventional machines, a very powerful starter capable `of bringing the turbine up to a h-igh rotational speed.

The passages of the impulse turbine hinder .back flow .of thegases, and this aids the starting .of the engine. In deed when a combustion chamber discharges alone .into the turbine, at the start, there can be no .back ow of the burnt gases through the turbine towards the rear of This phenomenon allows the starting of the turbine to be performed with only a single -combustionchamber in operation; furthermore it is not'necessary that all the pulsatory .chambers are in synchronisrn and they may have any sequence of operation.

One or more of the turbine 7wheels can be coupled to shafts independent from the shaft of .the A-air compressor .For instance, the impulse turbine 8 can drive .only fthe air compressor, whereas the constant pressure turbines y1i) This case .may .also1concern stationary electric power plants, for instance, or still propulsion plants for ships, locomotives or other vehicles. The turbine 8 combined if necessary with one of the wheels 10, can drive the air compressor, whereas one or more mechanically independent wheels 10 can drive an electric generator, the screws of a ship or the wheels of a l0como tive or other vehicle.

ln the case of a turbojet engine, amore or less important part of the energy contained in the gases which have performed work in the impulse turbine S, or even the whole of this energy, is used for accelerating these gases in the exhaust nozzle. in such a case, the constant pressure turbine l@ can only comprise one wheel or can even be altogether done without.

On the other hand, the embodiments described above only provide for a partial expansion corresponding to the pressure wave of the pulse, between the combustion chambers and the turbine 3, the remainder of the expansion being performed subsequently.

However, these embodiments wherein the pressure downstream of the impulse turbine 8 is equal to the discharge pressure P of the compressor, are not the only ones possible.

For instance, it is possible to design the turbine so that it operates with a certain expansion of the gases below P either through the distributor 7 the passages of which are then converging instead of having a constant cross-section, or preferably through the movable blading 8, the said turbine operating in the latter case with a certain degree of reaction. In this case, the pressure at the inlet of the nozzles of the constant inlet pressure turbines 10 is smaller than the discharge pressure of the compressor. The dilution air which is mixed with the gases before they ow into these turbines and is supplied through the apertures 11 will then provide not from the discharge of the compressor, but from a convenient intermediate stage of this compressor, through ducts different from the ducts 12 conveying air to the apertures 18, or else the whole of the dilution air from the discharge of the compressor will be mixed with the gases between their exhaust from the nozzles S and their inlet into the stator 7 of the primary turbine 8, the apertures 1S being conveniently proportioned for this purpose.

What We claim is:

l. A gas-turbine engine comprising in succession and in series ow arrangement, an air compressor, a compressed air manifold into which said compressor discharges, the pressure obtaining in said manifold being substantially constant, a pulse jet unit sucking air from said manifold, a velocity-absorbing turbine operated essentially by the kinetic energy of gas pulses issuing from said pulse jet unit, a gas exhaust manifold for collecting the exhaust gas of said turbine, the pressure obtaining in said exhaust manifold being substantially constant, and a power producing device designed for expanding the gas supplied thereto by said exhaust manifold.

2. A gas-turbine engine as claimed in claim l, further comprising a by-pass duct connecting the compressed air manifold with the gas exhaust manifold and lay-passing the pulse jet unit and the velocity-absorbing turbine, whereby the exhaust gas thereof is diluted with air in said exhaust manifold.

3. A gasturbine engine as claimed in claim 2, wherein the power producing device comprises a turbine of the constant inlet pressure type which is operated by diluted exhaust gas from the exhaust manifold.

4. A gasturbine engine as claimed in claim 2, wherein the power producing device comprises a jet propulsion nozzle.

5. A gas-turbine engine as claimed in claim 2, wherein the velocity-absorbing turbine is an impulse turbine, whereby the pressure obtaining in the exhaust manifold is substantially equal to the pressure obtaining in the compressed air manifold.

6. A gas-turbine engine as claimed in claim 2, wherein the velocity-absorbing turbine is a reaction turbine, whereby the pressure obtaining in the exhaust manifold is smaller than the pressure obtaining in the compressed air manifold.

7. A gas-turbine engine as claimed in claim 2, further comprising an ejector tube associated with the pulse jet unit and coaxally arranged at the outlet thereof, said ejector tube being adapted to suck air from the by-pass duct.

References Cited in the le of this patent UNITED STATES PATENTS 1,180,403 Leblanc Apr. 25, 1916 2,515,644 Goddard July 18, 1950 2,526,281 Ryan et al Oct. 17, 1950 2,543,758 Bodine Mar. 6, 1951 2,593,523 Bauger Apr. 22, 1952 2,612,749 Tenney Oct. 7, 1952 FOREIGN PATENTS 270 Q45 Switzerland Dec. 16, 1950 

